US2668669A - Apparatus for the explosive pulverization of coal - Google Patents

Description

Feb. 9, 1954 1 F, SKELLY 2,668,669

APPARATUS FOR THE'. EXPLOSIVE PULVERIZATION OF COAL Filed sept. 18, 1947 'ATTORNEYS atented Feb. 9, 195:4

APPARATUS FOR THE EXPLOSIV PULVERIZATION F COAL Joseph F. Skelly, New York, N. Y., assignor to The M. W. Kellogg Company, Jersey City, N. J., a

corporation of Delaware Application September 18, 1947, Serial No. 774,867

2 Claims.

This invention relates to the explosion pulverization or coal and more particularly to an improved method and apparatus for vertically classifying the explosion pulverization products in a mass of coal particles which is maintained in a fluidized condition by introducing the explosion products upwardly through said mass.

Recent developments of new products and processes employing nnely divided coal have been hampered in attaining commercial standing because of the high cost of reducing the coal to pulverized condition by methods heretofore known. For instance, a fuel comprised of oil containing colloidally suspended coal particles has been limited in application because no economic method was available for producing suficiently pulverized particles. It is a primary object of this invention to provide a commercially practicable method for powdering coal by explosion pulverization and an apparatus adapted for the employment of said method.

Although explosion pulverization has been previously prop-osed as a means for coniminuting permeable substances by permeating the particles with a uid under pressure and then suddenly reducing said pressure, such processes have never met with commercial success for the powdering of coal. One of the principal reasons for this failure has been that the pulverization process has been found to pulverize only a minor proportion of the particles subjected to the pressure reduction step. The balance of the particles must be recycled through the process for new treatment. It is an object of this invention to provide an eilicient and economical means for classifying the products of explosion pulverization into those particles which have been sufliciently pulverized and those which are adapted to be subjected to explosion pulverization. If desired, a third classification of the particles too large for explosion pulverization may be withdrawn for recycling to a preliminary mechanical grinder.

A further disadvantage of previously known explosion pulver-ization methods as applied to pulverizing coal, has been encountered in the diiilculty and cost of increasing the pressure on the granulated coal preparatory to explosion pulverization. An object of the present invention is to provide a method and apparatus by means of which known fluid pumping means may be employed to increase the pressure on said granulated coal material.

These objects and other objects, which will become apparent from the description of a typical application of the invention, are achieved by employing a large iuidized mass of particles which are maintained in a turbulent circulatory condi- A tion so that the particles therein classify themselves vertically with the heaviest particles near the bottom of said mass, the lightest particles in the upper portion of said mass, and particles of intermediate size according to elevation. In the preferred form of my invention this turbulent luidized condition of the mass of particles is maintained by introducing upwardly therethrough a mixture of particles and gas which is the product of explosion pulverization; that is, after the mixture of particles and the gaseous explosion pulverization medium have experienced a sudden reduction in pressure from a substantially elevated pressure to a pressure only slightly greater than that prevailing in the mass of fluidized particles, this mixture is introduced, usually through a plurality of openings through the bottom of a vessel containing the fluidized mass.

Although the invention may be employed for the explosion pulverization of materials other than coal, or for the explosion pulverization of coal and other materials with a great variety oi' vapors (mercury or Zinc vapors, for instance) or gases (such as air, nitrogen, or hydrocarbons), the process has been developed primarily for the explosion pulverization of coal by means of steam vapor, for which the process is uniquely adapted. It has been found that most coals have a crystalline structure and a degree of permeability such that it is desirable to apply the explosion pulverization method to coal granules of a predetermined maximum size, which may be found experimentally in the case of each particular type oi coal. For this reason, the system is uniquely valuable for explosively pulverizing coal on a large commercial scale. Furthermore, since steam is relatively cheap and non-reactive with coal, it is a preferred explosion medium for the presently disclosed process.

A typical embodiment of an apparatus suitable for practicing my method is illustrated in the accompanying drawing. Coal enters the apparatus at Iii and is ground in grinder II to a coarse feed powder (a number 4 mesh has been found quite suitable) and delivered to a large feed hopper I2 from the bottom of which the coarse coal is fed into a large vessel 53 containing a iluidized bed I4, the nature of which will be described in detail hereinafter. The feed may be introduced by a solids pump, a standpipe, or any other eiective device; in the present embodiment the elevation of the hopper I2 gives some standpipe effect; a spiral screw-type of feeding means is indicated diagrammatically at i5. The exact point in the vessel at which the feed is introduced is not very important, but in most cases best results are obtained by introducing the coarse powder into vessel I3 near the top of iluidized bed Ill.

The iluidized mass I4 is comprised of particles of coal which are maintained in a pseudo-liquid 3 or "iluidized bed by continuously introducing upwardly through said bed a gasiform iluidizing medium. 'The term Y'gasiform rather than gaseous is used here f'si-nce the Yiiu'idizing medium may -not be a true gas -but may be, for instance, a mixture of gas and solid particles which is much less denseV than the bed of particles Within vesseli and is capable of flowing thereinto and therethrough in,Y

the manner of a fluid under pressure. The fluidized condition thus produced in bed i4 'is 'characyterized by the relatively high concentration of particles of solid material per unit volume of occupied space, and maintained by the low velocity` oW of fluidizing medium upwardly through the bed. The maintenance of a denite minimum gaseous velocity is regarded as desirable to maintain "the bed in a turbulent 'fluidized state in which 'the-particles tend to A:move among one vanother in a 'circulatory manner. Preferably, the upward `velocity Aof the gas through the fluidized bed i4 is As'uiliciently high to -maintain sufficient turbulence in the bed so that any given elevation within Ves- -sel I;3, ythe smaller and lighter particles will tend 'to'drift in'an -upward direction and the larger and heavier vparticles in a downward direction with a result that the entire fluidized bed I4 tends to classify itself according to particle size ranging from the heaviest 4particles at the lowest point to the Ylightest particles vnear the upper surface i6 of iluidized bed I4. The optimum velocity of a `fluidizing medium, both with respect to its minimum and maximum value, will ibe dependent lupon the density, size, and shape of the solid :particles being iluidized and upon the properties :of lthe uidizing medium. Thus, for any particular'size or sizes of particles and quality of fluid- Yizing medium this velocity is adjusted within a range so -as'to maintain the desired turbulent but dense condition of fluid-bed I 4.

The finest particles `within the fluidizing bed Eli will Abe carried by the fluidizing medium, which the present preferred embodiment is composed principally of steam, upwardly from the surface i601 -fluidizing bed I 4 through line il. In the event that this overhead material is not as inely ground as desired, it may be passed to a separator I8 which will vremove coarse particles vand @return them to Vrvessel I3 Ithrough line i3. This l'separator may be of conventional design, such as cyclone separator of proper particle size selecltivity. It is best to return the oversized particles -frorn'this separator -to a point well below the tcp of the dense iluidized bed I@ to prevent their immediate reentrainment in the mixture of finely powdered coal by steam escaping through line i'i. 'Ihe nelypowdered overhead product withdrawn from Vessel I4 through line I'I and, if desired, freed of oversized particles from separator i8 is jthen passed by conduit'E to any suitable means 2i 'for separating the solid particles from the steam. The nely'pulverized coal product may be withdrawn from means 2l at 22 and the particle-free steam -may be withdrawn through line 23 to be 'reused in the process.

By far, the greater portion of the coal introduced into vessel I3 vthrough feeding means i5 will not be sufficiently fine to pass overhead through line I? and will settle downwardly l'through the vessel I3 to be classified at various elevations according to size as heretofore ldescribed. If desired, the heaviest particles may be withdrawn from the lower `portion of the vessel I3 and recycled to the grinder I I through conveyngrmeans 24. y

Those particles which are of a size adapted to the particular method of explosion pulverization being employed will tend to classify themselves at some particular elevation Ywii-,hirr iluidized mass I4. This elevation will focclur -dependent on the type of coal and the percentage of lines produced `by grinder I I. A plurality of withdrawal pipes 25, 26 and 27v are, therefore, provided for Withdra'wing iluidized coal from various elevations vwithin fluidized mass I4. The fluidized material so withdrawn is delivered to one or more lock hoppers 28 and 29; a pump 30 may be employed for this purpose, lhowever, in most instances it will be found preferable to eiect the movement of -luidized material Yfrom Iluidized bed I4 to lock hoppers 28, and 29 merely by a difference in pressure head.

In the preferred embodiment zone, fluidized material from vessel I3 --is introduced into lock hopper 28 through valve 3l at a relatively low pressure wln'le at the same time entrance of material into lock hopper 29 is prevented bythe closure of a valve 32. After lock hopper 28 is lled, valve 3| is closed and 32 is opened and fluidized material is Vpermitted to now from vessel I 3 into lock hopper 29. Lock hopper 28 is provided with outlet valve 33 which is closed while valve 3l is opened and hopper 28 is being lled, after which it is opened to permit iluidized products to flow -downwardly from the lower portion of hopper 28 into pipe 34 through which itis driven by steam at high pressure through an explosion pulverization nozzle 35 or any other'suitable means for suddenly reducing the pressure-on the fluidized material. From explosion pulverization means 35 the low pressure steam produced and the coal particles entrained therein are passed through line 36 to vessel I3, preferably through ports 37 in the bottom thereof, to flow upwardly through iiuidized bed I4 and maintain it in a fluidized condition.

After hopper 28 has been emptied, valves 32 and 33 are closed and atthe same time -valve3I-is opened to permit hopper 23v to be refilled and the outlet valve 42 of hopper 29 is opened to permit its contents to be subjected to high .pressure by the high-pressure steam in line 34 and-to permit flow of the high-pressure uidized material from hopper 29 into line 34 and thence to explosion pulverization means 35. Lock hoppers `28 Vand A29 are thus operated ultimately to maintain asubstantially continuous ilow of dense iluidized material from vessel I3 to one of the lock hoppers and a substantially continuous -ow of low-pres.- sure steam and explosion pulverization products from explosion pulverizationmeans 35 upwardly through ports 3l Yinto vessel I3. Steam entering vessel I3 through ports 3l is, of course, of sufficiently high pressure to overcome the pressure head existing because of the depth -of iluidized bed I4. Also, since the low-pressure steamand coal particles produced by the explosion pulverization means 35 are of much lower density than iluidized bed I4 and, therefore, serve admirably as a iluidizing medium. v I

The greater portion-of the high-pressure steam required to be introduced into line 34 for the eX- plosion pulverization step is obtained :by recompressing in compressor 38 the low-.pressure steam separated from the Apulverized product material by separator 2l. A steam generating source 3,9is provided for starting and forl providing vmake-up steam during the operation of the process vif necessary. It is desirable to provide a-sumpv40 at some point in the systemfor withdrawing from it condensed steam, which may bev recycled through a pipe 4I to the steam generating means 39. In operation, surface level I6 of dense Huidized mass I4 is maintained by continuously supplying through screw conveyor means I5 coarse coal ground by grinder II to a preliminary fineness. The iluidized bed I4 within vessel I3 is maintained at approximately the same volume and is of approximately the same character at all times during the operation of the process but material is constantly being withdrawn through lines 25, 26 and 27 or through any suitable combination of them to be fed alternately either to lock hopper 28 or 29; also, a much smaller quantity of material is being withdrawn as iinished or semi-iinished product through overhead line Il. Of course, only a minor fraction of material passing through explosion pulverization means 35 is reduced to the required iines and it therefore usually happens that the amount of material being withdrawn from vessel I3 for cycling through the explosion pulverization step is several times the amount which is being added during the corresponding period of time from hopper I2 or is being withdrawn through overhead line Il.

While one preferred form has been illustrated and described, this invention is not limited to the conventional details referred to. For instance, some iiuidizing means other than the explosion pulverization medium may be continuously pumped into the lower portion of vessel I3, withdrawn from the upper portion, above the surface IB of the dense phase of fluidized mass I4, and reintroduced into the lower portion. Such a iluidizing medium may be used independently of the steam, the latter being employed solely as an explosion pulverization medium. Also, the invention is not limited to a method or apparatus in which the materials are conveyed from one point to another in fluidized form. Lines 25, 26 and 2l may be any suitable means for transporting a classified material from vessel I3 to the explosion pulverization step. Similarly, the invention is not limited to the withdrawal of overhead product in fiuidized form; any suitable conveying means may be employed for withdrawing nely pulverized material from the uppermost layers of classifying vessel I3. Other parts of this system will also be found to be readily adaptable to other means of transportation to those skilled in the art. The regrinding of the coarsest material withdrawn from the lower portion of vessel I3 by line 24 is merely a suggestion which may be of advantage only in certain cases.

The invention is not limited to any particular means of explosion pulverization although it is peculiarly adapted to the combination of lock hoppers and explosion pulverization nozzle illustrated. The invention could be combined, however, with other means for raising the pressure on the coarse coal particles preliminary to explosion pulverization. For instance, the coarse coal particles may be formed into a slurry and pumped to a high pressure before being introduced into steam line 34, as described in the co-pending application Serial No. 774,768, now Patent No. 2,560,807, entitled Method and Apparatus for Explosion Pulverization, and filed by Walter E. Lobo.

I claim:

1. An apparatus for pulverizing material which includes: a vertically elongated vessel; means for introducing granulated solid material into the upper portion of said vessel; means for introducing a gasform suspension medium upwardly through said vessel to maintain particles therein in a turbulent iiuidized state to cause them to classify themselves vertically according to size; lock hopper means; means for withdrawing uidized solid particles from said vessel and transferring them to said lock hopper means; means for withdrawing said solid particles under pressure from said lock hoppers and introducing them into a high pressure gasiform medium to form a suspension and means for suddenly reducing the pressure thereon to produce explosive pulverization; means for reintroducing the gasiform medium and pulverized solid products from said explosion pulverization upwardly through said elongated vessel to maintain the contents thereof in the fluidized condition; means for withdrawing a nely pulverized product from the upper portion of said vessel; and means for withdrawing and recompressing gasiform medium from said vessel for reuse in said pressure reducing means.

2. An apparatus for pulverizing material which includes: a classification vessel; means for introducing granulated solid material into said vessel; means for introducing a gasiform suspension medium upwardly through said vessel to maintain particles therein in a turbulent fluidized state to cause them to classify themselves vertically according to size; lock hopper means; means for withdrawing fluidized solid particles from said vessel and transferring them to `said lock hopper means; means for withdrawing said solid particles under pressure from said lock hoppers and introducing them into a high pressure gasiform medium to form a suspension; means Vfor suddenly reducing the pressure thereon to produce explosive pulverization; means for reintroducing the gasiform medium and pulverized solid particles from said explosion pulverization upwardly through said elongated vessel to maintain the contents thereof in the iiuidized condition; and means for withdrawing a finely pulverized product from the upper portion of said vessel.

JOSEPH F. SKELLY.

References Cited in the ille of this patent UNITED STATES PATENTS Number Name Date 530,635 Blackman Dec. 11, 1894 1,748,920 Newhouse Feb. 25, 1930 1,791,100 Lykken Feb. 3, 1931 1,922,313 Mason Aug. 15, 1933 1,984,380 Odell Dec. 18, 1934 2,154,784 Stump Apr. 18, 1939 2,159,849 Graemiger May 23, 1939 2,310,894 Brusset Feb. 9, 1943 2,315,084 Chesler Mar. 30, 1943 2,318,306 Hanna May 4, 1943 2,337,162 McCleary Dec. 21, 1943 2,372,514 Pootjes Mar. 27, 1945 2,379,077 Harding June 26, 1945 2,421,212 Medlin May 27, 1947 2,560,807 Lobo July 17, 1951 2,568,400 Keargy Sept. 18, 1951 FOREIGN PATENTS Number Country Date 268,188 Great Britain Mar. 31, 1927 OTHER REFERENCES Chemical Engineering Progress (vol. 43, No. 8, pp. 429), title Fluidizing Processes."

Chem. 8; Met. Eng., Feb. 1941, pp. 122-125, 83 Exp. Dis.

Images